Gathering accurate, big-picture information on emissions from concentrated animal feedlot operations (CAFOs) is no easy task. If you live anywhere near a feedlot, you can imagine the challenge: some days it smells strongly; others, not at all. It's not just the wind that makes the difference, it's operations on those feedlots, which can vary greatly. But a new study out of NOAA in Boulder, which involved chemically "sniffing" the air downwind with sophisticated instruments, finds surprising similarities in the airborne emissions from feedlots. Their work promises to help scientists assess the effect of feedlots on air quality, as well as distinguish feedlot emissions from other sources. It can also help livestock owners identify which practices are most environmentally friendly.

"Feed, manure handling, composting, waste lagoons—all these practices affect the emissions," says Scott Eilerman, a CIRES researcher at CSD, and lead author on the study. "In the past, what we've done is take snapshot measurements – short-term projects that last from hours up to weeks." That provides researchers with lots of little measurements that give excellent small-scale detail. Alternatively, there have also been longer term measurements, taken while staying at a single spot over the course of a year. But those are also limited to a particular place.

"We wanted to bridge the gap between those two," explains Eilerman. So for a over a year, once every season, he and his colleagues piled into a mobile lab – a big van with a bunch of chemical and meteorological instruments installed in it – and motored around Weld County, Colorado. Using public roads, they drove near beef, dairy and sheep farms; they took turns driving for 24 hours straight, taking constant measurements day and night.

These new, detailed measurements showed, surprisingly, that there were consistent patterns of emissions downwind. "We developed a good picture of the daytime and nighttime emissions, which were consistent between all feedlots and between seasons," says Eilerman. To be clear they weren't measuring the amount of emissions; rather, they wanted to understand the ratios of one gas to another, for example, how much ammonia relative to methane and relative to nitrous oxide. Such ratios constitute a chemical "fingerprint," and this NOAA-led research team has used a similar technique to study the airborne impact of natural gas operations in northern Colorado and elsewhere.

Their results show that there is something of a "fingerprint" for CAFOs – a certain pattern to their emissions. That's critical, as it can help scientists attribute emissions to specific sources. "Lots of measurements at NOAA are aircraft campaigns," says Eilerman. "Let's say you're looking at methane and you want to look at emissions from oil and gas development. If you're picking up methane but it also has traces of ammonia, it means it's probably coming from feedlots, not oil and gas. This fingerprint really helps with source attribution."

Atmospheric emissions from animal husbandry are important to both air quality and climate, but are hard to characterize and quantify as they differ significantly due to management practices and livestock type, and they can vary substantially throughout diurnal and seasonal cycles. Using a new mobile laboratory, ammonia (NH3), methane (CH4), nitrous oxide (N2O), and other trace gas emissions were measured from four concentrated animal feeding operations (CAFOs) in northeastern Colorado. Two dairies, a beef cattle feedlot, and a sheep feedlot were chosen for repeated diurnal and seasonal measurements. A consistent diurnal pattern in the NH3 to CH4 enhancement ratio is clearly observed, with midday enhancement ratios approximately four times greater than nighttime values. This diurnal pattern is similar, with slight variations in magnitude, at the four CAFOs and across seasons. The average NH3 to CH4 enhancement ratio from all seasons and CAFOs studied is 0.17 (+0.13/-0.08) mol/mol, in agreement with statewide inventory averages and previous literature. Enhancement ratios for NH3 to N2O and N2O to CH4 are also reported. The enhancement ratios can be used as a source signature to distinguish feedlot emissions from other NH3 and CH4 sources, such as fertilizer application and fossil fuel development, and the large diurnal variability is important for refining inventories, models, and emission estimates.